1. Field of the Invention
The present invention relates to PWM control.
2. Description of the Related Art
One proposed PWM control technique is disclosed in Japanese Patent Laid-Open No. 2004-364366.
This related art technique forms a PWM fundamental wave from a basic frequency signal of a preset frequency and divides the frequency of the PWM fundamental wave to generate a PWM period signal. The PWM fundamental wave specifies a resolution to set a duty cycle in one period of the PWM period signal.
In a system of this related art technique, a change in frequency of the PWM fundamental wave for varying the accuracy of PWM control leads to a change in frequency of the PWM period signal. The changed frequency of the PWM period signal may coincide with a resonance frequency of a load structure (for example, a motor main body) under PWM control to cause undesirable vibration and noise.